The FDA requires the use of human hepatocytes for preclinical drug testing by pharmaceutical researchers, but unfortunately the supply of these cells is severely limited. Currently, cadaveric donors and surgical liver resection specimens are currently the only available source of human hepatocytes. These samples are very scarce and often yield cells of poor quality unsuitable for research. We have developed technology to massively expand fully functional primary human hepatocytes by serial transplantation in immune deficient FRGN mice in vivo. Hepatocytes isolated from these animals are highly viable and functional. Cell farming in FRGN mice allows the production of an unlimited supply of human hepatocytes for research in toxicology, drug metabolism, infectious disease, and cancer biology. The aims of this application are to optimize the isolation and storage of farmed hepatocytes and to fully validate their utility in comparison to the currently available cells. Once fully validated, these cells are going to be valuable in the commercial market.